Two masked gunmen shot one person dead during Sunday service at a church in Istanbul, Interior Minister Ali Yerlikaya said, adding that authorities were working to capture the assailants.
Yerlikaya said the attack, which Ankara condemned, took place around 0840 GMT at the Italian Santa Maria Catholic Church in the Sariyer district, and that one person - who was targeted by the gunmen - was killed while attending the service.
"A comprehensive investigation was launched on the matter and work has been started to capture the attackers," Yerlikaya said on social media platform X.
Speaking to reporters outside the church, Istanbul Governor Davut Gul said the victim was a Turkish national and that no one else was hurt. He said the attackers only fired at one person.
It was not immediately clear what the motive for the attack was or why the victim was targeted. Footage from the site showed several police cars and an ambulance outside the church.
President Tayyip Erdogan called the church's priest, a local administrator from his ruling party, and Poland's consul general in Istanbul to offer his condolences, his office said.
Pope Francis conveyed his condolences over the attack after his weekly Angelus prayer.
"I express my closeness to the community of Saint Mary Draperis Church in Istanbul that suffered an armed attack during mass that caused one death," he said.